Pile foundations consist of piles that are dug into soil till a layer of stable soil is reached. Pile foundations transfer building load to the bearing ground with thegreater bearing capacity. Pile foundations are useful in regions with unstable
upper soil that may erode, or for large structures.
Pile foundations are often required to resist lateral loading. Lateral loads come from a
variety of sources including wind, earthquakes, waves, and ship impacts. The lateral
capacity of a pile is usually much smaller than the axial capacity and as a result groups of
piles are often installed to increase the lateral capacity of the entire foundation system.
When vertical or plumb pile groups do not provide sufficient lateral resistance the piles
can be battered in order to mobilize some of the higher axial capacity to resist the lateral
load.

HISTORY OF PILE FOUNDATION:

Pile foundation have been used for many years, for carrying and transferring the loads to soil
considered to be weak in structure due to the soil conditions. In the early stages of development,
villages and towns were located in the close vicinity of lakes and rivers due to the availability of
water , and, also, to ensure proper protection of the area. Therefore, the weak bearing ground was
reinforced by the use of timber piles that were manually forced into the ground, or fixed into the
holes that were filled with stones and sand. The primitive methods of pile installation were
modified after the industrial revolution, and the techniques of installation by steam or diesel
driven machines were introduced. With the advancement in the technologies of soil mechanics
and other related disciplines, superior piles and pile installation system have been developed.

TENSION PILES:

Structures such as tall chimneys, transmission towers and jetties can be
subjected to large overturning moments and so piles are often used to resist the
resulting uplift forces at the foundations. In such cases the resulting forces are
transmitted to the soil along the embedded length of the pile. The resisting force can be increased in the case of bored piles by under-reaming. In the
design of tension piles the effect of radial contraction of the pile must be taken into account as this can cause about a 10% - 20% reduction in shaft resistance.

LATERALLY LOADED PILES:

Almost all piled foundations are subjected to at least some degree of
horizontal loading. The magnitude of the loads in relation to the applied
vertical axial loading will generally be small and no additional design
calculations will normally be necessary. However, in the case of wharves and
jetties carrying the impact forces of berthing ships, piled foundations to bridge
piers, trestles to overhead cranes, tall chimneys and retaining walls, the
horizontal component is relatively large and may prove critical in design.
Traditionally piles have been installed at an angle to the vertical in such cases
providing sufficient horizontal resistance by virtue of the component of axial
capacity of the pile which acts horizontally. However the capacity of a vertical
pile to resist loads applied normally to the axis, although significantly smaller
than the axial capacity of that pile, may be sufficient to avoid the need for
such 'raking' or 'battered' piles which are more expensive to install. When
designing piles to take lateral forces it is therefore important to take this into account.

The spacing of the base of the battery and the friction of the skin in a group of batteries decides the design of the base of the battery, its efficiency and capacity in any construction. A pile is basically a long cylinder of a strong material like concrete that is pushed into the ground to act as a constant support for structures built on top of it.
Battery bases are used in the following situations:
1. When there is a weak soil layer on the surface. This layer can not support the weight of the building, so the building loads have to pass over this layer and be transferred to the stronger soil layer or rock that is below the weak layer.
2. When a building has very heavy and concentrated loads, such as in a high-rise structure, bridge or water tank.

The foundations of piles are able to support loads higher than the scattered shoes.

There are two fundamental types of pile foundations (based on structural behavior), each of which functions in its own way.
End Bearing Batteries

In the end bearing piles, the lower end of the pile rests on a particularly strong layer of soil or rock. The building load is transferred through the pile over the strong layer. In a sense, this heap acts like a column. The key principle is that the lower end rests on the surface, which is the intersection of a weak and strong layer. Therefore, the charge ignores the weak layer and is safely transferred to the strong layer.

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